1. Field of the Invention
The present invention relates to a phase adjuster circuit and a phase adjusting method, and more particularly to accurate phase adjustment of a reference signal used for minute signal amplification.
2. Description of Related Art
There is a method using synchronous detection as means for amplifying a minute signal that is obtained from a sensor 111. FIG. 13 shows a synchronous detection circuit 100 according to a related art. A carrier wave RS is outputted from an oscillator 112 as a transmission carrier wave of a sensor signal. In the sensor 111, the carrier wave RS is subjected to amplitude modulation. A signal that has been subjected to amplitude modulation is amplified by an amplifier 116, and then inputted to a synchronous detection circuit 115. Also, in a phase adjuster circuit 101, a phase of the carrier wave RS is shifted. In general, the phase of the carrier wave RS is shifted by 90°. Also, as the phase adjuster circuit 101, there is used a differentiation circuit using a capacitor and a resistant element, or a delay circuit. Synchronous detection is conducted in the synchronous detection circuit 115. A detection signal DS that is outputted from the synchronous detection circuit 115 is inputted to a low pass filter 113. A demodulation signal DTS is outputted from the low pass filter 113 and then inputted to an amplifier 117. An output signal VOUT is outputted from the amplifier 117. With the above structure, only an original signal component of the sensor 111 is detected.
The above related art is disclosed in Japanese Unexamined Patent Publication No. H04(1992)-267620, Japanese Unexamined Patent Publication No. H10(1998)-31032, Japanese Unexamined Patent Publication No. S60(1985)-194820, and Japanese Unexamined Patent Publication No. H04(1992)-168803.